Tactile vision substitution systems (TVSS) are used to deliver image information to the brain via an array of stimulators in contact with the skin in one of several parts of the body, for example, the abdomen, the back, the thigh or the fingertip. Points of the image are mapped to individual stimulators in the array as either vibrations or direct electrical excitation. With training, perceptual judgments normally used for vision such as depth judgment can be applied to these tactile images. A summary of the art in this field is provided in a paper by the present inventors, hereby incorporated by reference, entitled: Electrotactile and Vibrotactile Displays for Sensory Substitution Systems, IEEE Transactions on Biomedical Engineering, Volume 38, No. 1, January 1991.
The delay in perception for tactile arrays is less than that for vision. For this reason, TVSS systems are not only promising as rehabilitative strategies for sight-impaired individuals but offer an alternative human/machine interface for sighted individuals, especially where rapid reaction times are required.
Unfortunately, current TVSS systems have been limited in practical application. Mechanical vibrotacter systems in which the stimulators vibrate are bulky and require considerable energy. Electrotactile systems in which the stimulators produce direct electrical stimulation require relatively high voltage, especially in areas of the fingertips, because there are protective layers of skin between skin surface and the skin""s sensory receptors. TVSS systems which use the fingertips as a reception site, limit the use of the hands for other tasks whereas systems using a site such as the abdomen require larger arrays, are less convenient, and require a conductive gel for proper operation.
The present invention provides an improved human/machine interface (HMI) system using the tongue as a stimulation site. The tongue contains a large number of nerve endings, thus permitting the construction of a small array with a high number of stimulators. Preliminary data by the inventors shows that users tend to adapt or accommodate stimulation current over time when that current is applied to the fingertip requiring the stimulation current or voltage to be increased. In contrast, it presently appears that subjects maintain a constant or even slightly decreasing current level for tongue stimulation.
Specifically the present invention provides a tactile stimulation array for the tongue having a mouth part sized to be received and stabilized within the mouth and an array of tactile elements positioned over a lower surface of the mouth part to be in contact with the tongue when the mouth part is received within the mouth. Excitation circuitry communicates with the tactile elements and receives a spatially encoded signal to excite selected ones of the tactile elements according to the spatial encoding.
Thus it is one object of the invention to provide an improved human/machine interface for communicating spatially encoded information, such as but not limited to, image information to the tongue as an alternative to optical displays.
The tactile elements may be electrodes and the excitation circuitry may connect the electrodes to a source of electrical power to excite selected ones of the tactile elements.
Thus it is another object of the invention to make use of the improved electrical sensitivity offered by the tongue both because of the location of the tongue""s sensory receptors close to its surface and the presence of saliva as a conductor. Experimentation by the present inventors has suggested that the tongue requires only about three percent of the voltage and far less current than, for example, the fingertip, to achieve equivalent sensation levels.
The spatially encoded signal may include a plurality of data points having defined locations and magnitudes and the excitation circuit may map data points to tactile elements having corresponding locations and excite the tactile elements with an electrical pulse according to a function having the data point magnitude as a range and a value selected from the group of: pulse amplitude, pulse duration, and pulse frequency content.
Thus it is another object of the invention to provide a multi-dimensional display where each point of stimulation may have a varied intensity based on a variety of factors. To the extent that the tongue may distinguish simultaneously between these factors, a multidimensional stimulus may be obtained.
The mouth part may include an upwardly concave plate supporting on its lower surface the tactile elements and sized to fit beneath the hard palate.
Thus it is another object of the invention to provide an array that minimizes interference with tongue function. The tongue is highly mobile and may be moved against and away from a tongue based array as required.
The upwardly concave plate may be flanked at its lateral edges by bite bars wherein the mouth part may be stabilized within the mouth by a pressing of the bite bars between the teeth. Alternatively, a dental retainer design may be used with wire brackets engaging the teeth.
It is thus another object of the invention to allow an array that is easily placed within or removed from the mouth and stabilized there and then removed at will.
The mouth part may be a nipple sized to be stabilized within the mouth of a sucking infant.
Thus it is another object of the invention to allow the array to be adapted for infant use as part of a pacifier or the like to provide needed stimulation for sight impaired babies.
The array may include a receiver communicating with the excitation circuitry in receiving the spatially encoded signal as a radio wave.
It is thus another object of the invention to allow the array to be entirely contained within the mouth without obstructing or cumbersome electrical leads. Because electrical stimulation of the tongue requires only about three percent of the voltage as required by the fingertip and much less current, self-contained battery operation is possible.
The foregoing and other objects and advantages of the invention will appear from the following description. In this description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration, the preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention.